An in situ assessment of selenium bioaccumulation from water-, sediment-, and dietary-exposure pathways using caged chironomus dilutus larvae



An in situ caging study was conducted downstream of a metal mine in northern Canada to determine the significance of surface water versus sediment exposure on selenium (Se) bioaccumulation in the benthic invertebrate Chironomus dilutus. Laboratory-reared C. dilutus larvae were exposed to either site-specific whole-sediment and surface water or surface water only for 10 d at sites with differing sediment and Se characteristics. Results showed elevated whole-body Se concentrations in C. dilutus larvae when exposed to sediment and water, compared with larvae exposed to Se in the surface water only at concentrations ranging from <1 µg Se/L to 12 µg Se/L. In response to these findings, a second in situ experiment was conducted to investigate the importance of dietary Se (biofilm and detritus) versus whole-sediment-exposure pathways. Larvae exposed to sediment detritus had the highest Se concentrations after 10 d of exposure (15.6 ± 1.9 µg/g dry wt) compared with larvae exposed to whole-sediment (12.9 ± 1.7 µg/g dry wt) or biofilm (9.9 ± 1.6 µg/g dry wt). Detritus and biofilm appear to be enriched sources of organic Se, which are more bioaccumulative than inorganic Se. Midge larvae from the reference treatment contained elevated concentrations of diselenides (i.e., selenocystine), while larvae from the biofilm treatment had the highest concentrations of selenomethionine-like compounds, which may be a biomarker of elevated Se exposures derived from anthropogenic sources. Whenever possible, Se concentrations in the organic fraction of sediment should be measured separately from whole-sediment Se and used for more accurate ecological risk assessments of potential Se impacts on aquatic ecosystems. Environ Toxicol Chem 2013;32:2836–2848. © 2013 SETAC